The cytotoxicity of periodontopathic bacteria will be investigated with primary emphasis on two bacteria associated with juvenile periodontis (Capnocytophaga sputigena, strain 4 and Actinobacillus actinomycetemcomitans, strain Y4). The isolation, characterization and mechanism(s) of action of two cytotoxic factors will be examined: the proliferation inhibition factor (PIF) of C. sputigena which inhibits growth and metabolism of gingival fibroblasts in tissue culture and the Actinobacillus leukotoxic factor (ALF) which is cytotoxic for human polymorphonuclear leukocytes. The isolation, purification and characterization of each factor will be monitored and analyzed by physico-chemical, immunological and other appropriate biological criteria (lactic dehydrogenase release from PMNs, inhibition of fibroblast growth in vitro, ultrastructural changes in affected host cells). The environmental and cultural conditions affecting the synthesis and activity of these bacterial virulence factors will also be determined. Once the details of chemical composition of the factors and the methods of their extraction from bacteria are established it is proposed to survey other known periodontopathic gram negative bacteria for similar evidences of cytotoxic potential. These studies dealing with the direct cytotoxic effects of crevicular bacteria and their products offer another approach to understanding the nature and causes of tissue destruction in periodontal disease.